Apparatus for calibrating an analogue screen display system

Abstract

Apparatus for use in calibrating a display system comprising digital-to-analogue converters (D.A.C) (11,12,13) for converting a digital colour control signal to analogue colour component signals which are suitable for controlling an electronic display. An analogue signal modifier modifies the signals from the D.A.C. The apparatus also comprises a switch (10) for connecting between the D.A.C. and the analogue signal modifier. The switch is operable in a first mode (52,54) to pass signals from the D.A.C. (11,12,13) directly to the analogue signal modifier or in a second mode (53) to pass analogue calibration colour component signals to the analogue signal modifier such that the appearance of the signals from the D.A.C. and the calibration signals can be visually compared on a screen (17) to determine whether any reproduction errors are in the D.A.C. (11,12,13) or in the signal modifier.

We claim: 
     
       1. Apparatus for use in calibrating an analogue display system comprising: digital-to-analogue conversion (D.A.C.) means for converting digital color control signals to analogue colour component signals suitable for controlling an electronic display, and analogue signal modifying means for modifying the analogue colour component signals from the D.A.C. means and connected to a screen of the analogue display system; the apparatus further comprising:   switch means connected to said D.A.C. means and said analogue signal modifying means said switch means including means for producing analogue calibration color component signals, said switch means being operable in a first simultaneous display mode to pass said analogue colour component signals from said D.A.C. means directly to said analogue signal modifying means and operable in a second simultaneous display mode to pass said analogue calibration colour component signals to said analogue signal modifying means such that an appearance of said analogue colour component signals from said D.A.C. means and an appearance of said analogue calibration colour component signals can be visually compared on the screen of the analogue display system to determine whether any reproduction errors are in said D.A.C. means or in said analogue signal modifying means.   
     
     
       2. Apparatus according to claim 1, further comprising means for producing average analogue colour component signals having a value equal to an average of the analogue colour component signals of the first simultaneous display mode to provide an average signal area on said screen wherein said switch means is operable in a third simultaneous display mode to pass said average analogue colour component signals to said analogue signal modifying means such that an appearance of said average analogue colour component signals can be visually compared to the appearance of said analogue colour component signals from said D.A.C. means and the appearance of said analogue calibration colour component signals on said screen of said analogue display system. 
     
     
       3. Apparatus according to claim 2, wherein a ramp function is applied to the average analogue colour component signals to provide a variation between black and white across at least a part of said average signal area. 
     
     
       4. Apparatus according to claim 1, wherein a ramp function is applied to said analogue colour component signals of the first simultaneous display mode. 
     
     
       5. Apparatus according to claim 1, wherein each said analogue calibration colour component signal of the second simultaneous display mode input to said analogue signal modifying means for a calibrated white signal results in an output from said analogue signal modifying means of 0.7 volts. 
     
     
       6. Apparatus according to claim 1, wherein each said analogue calibration colour component signal of said second simultaneous display mode input to said analogue signal modifying means for a calibrated black signal results in an output from said analogue signal modifying means of 0 volts. 
     
     
       7. Apparatus according to claim 1, wherein the analogue colour component signals on the first simultaneous display mode comprise a white colour control signal input and the analogue calibration colour component signals of the second simultaneous display mode comprise a calibrated white display.